DESCRIPTION (applicant's abstract): A striking feature of sleep is the gradual silencing of noradrenergic (NA) and serotonergic (5-HT) neurons in brainstem locus coeruleus (LC) and dorsal raphe nuclei (DRN) as an animal passes from wakefulness (W) to non-rapid-eye movement sleep (NREM) to rapid eye-movement sleep (REM). This silencing is currently thought to be necessary for REM. However, in cats with pontine lesions that create the phenomenon of REM without atonia (REM-A), DRN neurons can resume a relatively high rate of firing. In REM-A, animals can exhibit elaborate behavior (head- lifting; righting on forelimbs, "orienting" [some can orient to external stimuli], standing and locomotion). Thus, the role of 5-HT during REM may involve motor aspects of state control. The fate of NA LC neurons in REM-A is unknown. In W, NA LC neurons have roles in orienting and motor behavior whereas they are silent in normal REM. This project will (l) compare REM and REM-A in rats and (2) study the activity of NA LC cells in REM and in REM-A. The latter is a state in which many electrophysiological characteristics of REM, when NA cells normally would be silent, co-occur with orienting-like behavior that, in W, could be associated with their activation. This approach will allow us to address a question fundamental to our understanding of REM: Is the silence of NA neurons necessary for REM? We shall thoroughly describe the behavior of REM-A in rats and determine their ability to respond overtly to neutral and significant external stimuli. We shall then determine the relationship of NA LC neurons to spontaneously emitted and externally elicited stimuli in REM-A. These studies will provide information as to whether the silence of these neurons is necessary for REM, or whether it is associated with the behavioral suppression created by the atonia of normal REM. These studies may lead to a better understanding of disorders of REM, such as REM behavior disorder, which, like REM-A, is characterized by overt behavior during sleep.